CN109689739B

CN109689739B - Molding material comprising ethylene-vinyl ester copolymer saponified material pellet group and molding method using same

Info

Publication number: CN109689739B
Application number: CN201780055075.1A
Authority: CN
Inventors: 西村大知; 畑中诚; 碓氷真太郎
Original assignee: Mitsubishi Chemical Corp
Current assignee: Mitsubishi Chemical Corp
Priority date: 2016-09-07
Filing date: 2017-08-28
Publication date: 2022-11-08
Anticipated expiration: 2037-08-28
Also published as: US20190202952A1; JP7087388B2; JPWO2018047661A1; EP3511361B1; CN109689739A; EP3511361A1; EP3511361A4; WO2018047661A1

Abstract

An object of the present invention is to provide: a molding material comprising an EVOH resin pellet group having excellent feedability when melt extrusion molding is performed. The present invention is a molding material comprising a pellet group having at least 20 pellets of an ethylene-vinyl ester copolymer saponified material, wherein each pellet constituting the ethylene-vinyl ester copolymer saponified material pellet group is a pellet having a surface formed with a single closed curved surface, and when the maximum outer diameter of the pellet is defined as a major diameter and the minimum diameter in a cross section of the maximum area in a cross section perpendicular to the major diameter is defined as a minor diameter, the average value of the major diameter/minor diameter ratio of the pellets 20 taken out from the pellet group is 1.6 or less, and the standard deviation of the major diameter/minor diameter ratio is 0.13 or less.

Description

Molding material comprising ethylene-vinyl ester copolymer saponified material pellet group and molding method using same

Technical Field

The present invention relates to a molding material comprising a group of pellets of an ethylene-vinyl ester copolymer saponified product (hereinafter referred to as "EVOH resin") and a molding method using the same, and more particularly, to a molding material comprising a group of pellets of an EVOH resin excellent in feedability at the time of melt extrusion molding and a molding method using the same.

Background

EVOH resin is a thermoplastic resin having high crystallinity due to hydrogen bonds between hydroxyl groups present in the side chains of the polymer, and further having high intermolecular force in the amorphous portion. With such a structure, a film using an EVOH resin exhibits excellent gas barrier properties, and can be used for various applications by melt molding.

EVOH resins used as molding materials are generally distributed as cylindrical or granular pellets having a length of about 1 to 10mm. EVOH resin pellets are generally produced by strand cutting. The wire cutting mode is as follows: EVOH resin pellets are produced by extruding a solution obtained by dissolving EVOH resin (or a composition thereof) in a suitable solvent into a coagulating liquid from a metal plate having a hole with a diameter of about 1 to 5mm, or extruding a heated and molten resin into a die, cooling and solidifying the resin to obtain a rod-shaped strand, and cutting the rod-shaped strand into a predetermined size with a cutter.

In the melt extrusion molding using the EVOH resin pellet, particularly, when the molten resin in the melt plasticizing part flows, there are the following problems: a problem of so-called poor feeding properties, which is caused by vibration of the screw in the screw flow path constituting the melt plasticizing section or occurrence of noise due to torque variation during extrusion of the resin. Such a state of sound generation is a state of load on the screw, and therefore, in a bad case, there is a fear that abrasion of the screw or mixing of abrasion powder into the molten resin is caused. In addition, the mixing of the abrasive powder into the molten resin causes deterioration in the quality of a molded product such as a film.

As a technique for solving the above problems, a technique for producing pellets by thermal cutting has been proposed (for example, see patent documents 1 and 2). In patent document 1, EVOH in a water-containing molten state discharged from a discharge port 31 of a twin-screw extruder is extruded from a die 32, and immediately cut by rotation of a rotary knife 33. Cooling water 37 is supplied into the cutter casing 35 from a cooling water supply port 36 to form a water film 38, the pellets immediately after cutting are cooled, and cooling water and pellets 40 are discharged from a pellet discharge port 39 (see paragraph [ 0016 ] and fig. 2).

In patent document 2, an EVOH solution is fed into a filter device (2) through a feed pipe (1) by using a fluid transfer means (14), and then fed into a die (3) of an extrusion molding machine, the EVOH solution having passed through the die (3) immediately enters a cutter body (5), and is cut by a cutter blade (4) to form EVOH solution pellets (see paragraph [ 0017 ] and fig. 1).

In the hot cutting method, since the cutting is performed in a state of molten resin, in the process of cooling and solidifying after the cutting, the resin sags at the edge portion formed by the cutting, and a round pellet having no corner can be obtained by the surface tension of the resin. In the case of such pellets having no corners, the flowability in the screw flow path constituting the melt plasticizing section becomes good, and therefore, the occurrence of abnormal noise can be reduced as compared with the abnormal noise generated when pellets obtained by strand cutting are used.

As another technique for solving the above problems, a molding material in which 2 kinds of EVOH resin pellets having different ethylene contents are mixed has been proposed (for example, see patent document 3). The molding material described in patent document 3 is a molding material including an EVOH resin pellet group, each pellet constituting the EVOH resin pellet group is a pellet having a substantially circular or elliptical cross section, the pellet group is a pellet mixture including a1 st EVOH resin pellet having an ethylene unit content of 20 to 34 mol% and a2 nd EVOH resin pellet having an ethylene unit content of 35 to 60 mol%, and a difference in ethylene unit content between the 1 st EVOH resin pellet and the 2 nd EVOH resin pellet is 10 to 30 mol% (see paragraph [ 0024 ]).

By using such a molding material in which 2 kinds of EVOH resin pellets are mixed, fluidity in a screw flow path constituting a melt plasticizing portion becomes good (see paragraph [ 0079 ]), and therefore, occurrence of abnormal noise can be reduced as compared with abnormal noise generated when pellets obtained by strand cutting are used.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open No. 2001-96530

Patent document 2: japanese Kokai publication 2006-524144

Patent document 3: japanese patent laid-open No. 2015-143349

Disclosure of Invention

Problems to be solved by the invention

When pellets obtained by the thermal cutting method proposed in patent documents 1 and 2 are used, although the occurrence of abnormal noise can be reduced as compared with the case of using pellets obtained by the strand method, the generation of abnormal noise is still caused, and therefore, further improvement is required.

In the case of the molding material proposed in patent document 3, the ethylene content cannot be applied to the case where a single EVOH molding material is desired, and there is room for improvement.

The present invention has been made in view of the above problems, and an object thereof is to provide: a molding material comprising an EVOH resin pellet group having excellent feedability when melt extrusion molding is performed, and a molding method using the molding material.

Means for solving the problems

When the EVOH resin is cut with a cutter while being melt-extruded or cooled and solidified, the edge portion resulting from the cutting may sag during the cooling and solidification process and may be spherical due to surface tension to function, and therefore, pellets having a single closed curved surface on the surface can be obtained. Specifically, depending on the shape (usually a quadrangular prism or a cylinder) in which melt extrusion is performed, pellets having a shape of a sphere, a disk, a rugby, a chestnut, or the like including an ellipsoid in cross section, and pellets having a tear drop shape, a spherical shape, or the like are rarely obtained.

The present inventors have studied the shape of pellets for improving the feeding property in melt extrusion molding, and have focused on the fact that if pellets having a shape closer to a spherical shape and less variation in shape are used, the feeding property is improved, and the specific shape of the pellets is specified, thereby achieving the present invention.

That is, the present invention is a molding material comprising a pellet group including at least 20 pellets of an ethylene-vinyl ester copolymer saponified product, wherein each pellet constituting the ethylene-vinyl ester copolymer saponified product pellet group is a pellet having a surface formed by a closed curved surface, and when a maximum outer diameter of the pellet is defined as a major diameter and a minimum diameter in a cross section of a maximum area in a cross section perpendicular to the major diameter is defined as a minor diameter, an average value of a major diameter/minor diameter ratio of the pellets 20 taken out from the pellet group is 1.6 or less, and a standard deviation of the major diameter/minor diameter ratio is 0.13 or less.

In the present invention, it is preferable that each of the pellets constituting the saponified ethylene-vinyl ester copolymer pellet group is oval in cross section perpendicular to the major axis.

Further, the water content of the pellet group is preferably 0.5 wt% or less.

In the present invention, it is preferable that the average value of the major axis is 1 to 20mm and the average value of the minor axis is 1 to 10mm among 20 pellets taken out from the pellet group.

The present invention also provides a molding method using the molding material. That is, the present invention is a molding method characterized by feeding the molding material to an extruder having a screw rotation speed of 10 to 100rpm and molding the molding material into a molded article.

The molding material of the present invention is a molding material containing an EVOH resin pellet group having a shape closer to a spherical shape and having little variation in shape, and therefore, the feeding property at the time of melt extrusion molding can be improved.

In order to obtain an EVOH pellet group having a shape closer to a sphere and having little variation in shape among the pellets having no corners, it is necessary to use a method having poor production efficiency, and therefore, it is common for those skilled in the art to avoid such a production method, and a molding material as in the present invention has not been used.

ADVANTAGEOUS EFFECTS OF INVENTION

The molding material of the present invention is a molding material containing an EVOH resin pellet group having a shape closer to a spherical shape and having little variation in shape, and therefore, according to the present invention, the feeding property at the time of melt extrusion molding is improved. In addition, since the mixing of the abrasion powder into the molten resin can be suppressed, the quality of the molded product such as a film can be improved.

Drawings

Fig. 1 is a schematic view for explaining the major and minor diameters in the pellet P which is an ellipsoid.

FIG. 2 (a) is a plan view of an EVOH resin pellet of an example, and FIG. 2 (b) is a plan view of 20 EVOH resin pellets whose major and minor diameters are measured.

FIG. 3 (a) is a plan view of an EVOH resin pellet of a comparative example, and FIG. 3 (b) is a plan view of 20 EVOH resin pellets in which the major and minor diameters are measured.

Detailed Description

The present invention is a molding material comprising a pellet group having at least 20 pellets of an ethylene-vinyl ester copolymer saponified material, wherein each pellet constituting the ethylene-vinyl ester copolymer saponified material pellet group is a pellet having a surface formed with a single closed curved surface, and when the maximum outer diameter of the pellet is defined as a major diameter and the minimum diameter in a cross section of the maximum area in a cross section perpendicular to the major diameter is defined as a minor diameter, the average value of the major diameter/minor diameter ratio of the pellets 20 taken out from the pellet group is 1.6 or less, and the standard deviation of the major diameter/minor diameter ratio is 0.13 or less.

< pellets whose surface is formed of a closed curved surface >

Each pellet taken out from the group of EVOH resin pellets constituting the molding material of the present invention is a pellet having a surface constituted by one closed curved surface. "the pellet whose surface is constituted by one closed curved surface" means in other words, 1) the pellet whose surface is constituted by a curved surface as a whole; 2) A pellet having no corner formed by joining a plurality of faces; 3) The cross section of the pellet at any position does not become a rectangular pellet. Here, the "closed curved surface" refers to a continuously curved surface generated by curved movement, and is a curved surface closed like a spherical surface.

The pellet is preferably a pellet having an elliptical cross section perpendicular to the major axis, which will be described later. Here, "oval" includes: egg-shaped, oblong, oval, and curvilinear shapes that approximate these shapes.

The pellets are indefinite in shape and have a slight difference in shape, but generally have a shape including an ellipsoidal spherical shape, a disk shape, a rugby ball shape, a chestnut shape, and there may be a few teardrop-shaped or spherical pellets.

< major and minor diameters of pellets >

The average value of the aspect ratio of 20 pellets taken out of the EVOH resin pellets constituting the molding material of the present invention is 1.6 or less, and the standard deviation of the aspect ratio is 0.13 or less.

Here, the major axis of the pellet means the maximum diameter when the pellet is observed in a three-dimensional manner. The short diameter of the pellet means the smallest diameter in a cross section perpendicular to the long diameter and having the largest area. For example, when the cross section is circular, the minor axis is the length of the diameter, and when the cross section is elliptical, the minor axis is the length of the minor axis.

Here, the description will be specifically made with reference to fig. 1. In fig. 1, for ease of understanding, the granular material P is illustrated as an ellipsoid. The maximum outer diameter when the pellet P is three-dimensionally observed is "a", and therefore, the major axis is "a". Then, the cross section perpendicular to the major axis and having the largest area becomes a cross section F located at the midpoint of the major axis. Since the cross section F is an ellipse, the length of the major axis is "b" and the length of the minor axis is "c", the minimum diameter of the cross section F is "c" and the minor axis is "c".

From the above, the pellet P shown in fig. 1 has a major axis "a" and a minor axis "c", and thus the major axis/minor axis ratio is "a/c".

In the present embodiment, the average value of 20 pellets is used for both the major diameter and the minor diameter.

< method for measuring Long diameter and short diameter >

The average value of the ratio of the major axis to the minor axis of 20 pellets taken out from the pellet group constituting the molding material of the present invention is 1.6 or less, preferably 1.1 to 1.5, and particularly preferably 1.2 to 1.4. When the above value is too large, the feeding property and the discharge stability tend to be poor when the resin composition is subjected to melt extrusion molding, and when the value is within the above range, the effect of the present invention tends to be more effectively obtained.

Further, the average of the major axis and the minor axis of 20 pellets taken out from the pellet group constituting the molding material of the present invention is preferably 1 to 20mm, particularly preferably 3 to 6mm, and 2 to 6mm, more preferably 3.5 to 5.5mm, and 5 to 5.5mm. When the value is within the above range, the effects of the present invention tend to be more effectively obtained.

The method for measuring the major axis and the minor axis includes, for example, the following methods: the pellet is taken in a hand and observed, and after a long diameter is measured using a measuring instrument such as a vernier caliper, a cross-sectional position at which the maximum area is obtained in a cross section perpendicular to the long diameter is visually and tactually recognized, and a short diameter at the time of assuming the cross section is similarly measured.

< method for calculating standard deviation of major axis/minor axis ratio >

In the present embodiment, the major axis and minor axis of 20 pellets taken out from the pellet group constituting the molding material of the present invention are measured to determine the major axis/minor axis ratio, and therefore, the standard deviation is determined for the 20 pellets.

When the major axis/minor axis ratio of the 20 pellets is Xi (i =1 to 20) and the average value of the major axis/minor axis ratio is Xave, the standard deviation S is obtained by the following equation (1).

Standard deviation S = √ { (X1-Xave) ² +(X2-Xave) ² +…+(Xi-Xave) ² +…+(X19-Xave) ² +(X20-Xave) ² }/20〕···(1)

The standard deviation of the ratio of the major axis to the minor axis of 20 pellets taken out from the pellet group constituting the molding material of the present invention is 0.13 or less, preferably 0.05 to 0.13, and particularly preferably 0.10 to 0.12. When the above value is too large, the feeding property and the discharge stability tend to be lowered when the resin composition is subjected to melt extrusion molding, and when the value is within the above range, the effect of the present invention tends to be more effectively obtained.

The weight of the pellets constituting the molding material of the present invention is usually 10 to 40mg, preferably 15 to 35mg, particularly preferably 15 to 30mg, per 1 pellet. The pellets are stored in a container such as a bag, a can, or a container, and subjected to a molding step. That is, about 63 to about 250 ten thousand pellets are usually sealed in a 25kg package containing the molding material of the present invention. In the present invention, 20 pellets were arbitrarily taken out from the pellet group constituting the molding material and subjected to the above measurement.

The pellets taken out of the pellet group constituting the molding material of the present invention have a surface formed of a single closed curved surface, in other words, a pellet having a curved surface as a whole, and have a shape close to a spherical shape and less variation in shape than conventional pellets. This is because, when a very small amount of 20 pellets is measured as a sample with respect to a pellet group containing an unspecified large amount of pellets constituting the molding material of the present invention, the pellets satisfy the average value and standard deviation defined in the present invention in any part within the pellet group. That is, the molding material of the present invention has less variation in shape as the whole of the pellets contained in the pellet group.

< method for measuring Water content >

The water content of the pellet group constituting the molding material of the present invention is preferably 0.5% by weight or less, particularly preferably 0 to 0.3% by weight, and more preferably 0 to 0.25% by weight.

The water content of the pellets was measured by the following method.

First, 10g of the pellets were taken out into an aluminum cup, and the weight of the aluminum cup monomer (weight: C1) and the weight of the aluminum cup to which the pellets (weight: P1) were added (C1 + P1) were measured, respectively. Then, the aluminum cup containing the pellets was subjected to nitrogen substitution, and heat treatment was performed at 150 ℃ for 5 hours in a commercial dryer (SAFETY OVEN SPH-100, manufactured by TABAI ESPEC CORPORATION) without vacuum evacuation. After the heat treatment, the aluminum cup containing the pellets was taken out from the dryer, allowed to stand still in the dryer containing a drying agent for 30 minutes, the temperature of the pellets was returned to room temperature, the weight (C1 + P2) of the aluminum cup containing the heat-treated pellets (weight: P2) was measured, and the water content (wt%) was calculated from the following equation (2).

Moisture content (% by weight) = { (C1 + P1) - (C1 + P2) }/{ (C1 + P1) -C1} ]. Times.100 { (P1-P2)/P1 }. Times.100. Cndot. (2)

< pellets of ethylene-vinyl ester copolymer saponified product (EVOH resin) >

(1) EVOH resin

The saponified ethylene-vinyl ester copolymer (EVOH resin) used as the molding material of the present invention is a saponified ethylene-vinyl ester copolymer obtained by copolymerizing ethylene and a vinyl ester monomer and then saponifying the copolymer, and is a water-insoluble thermoplastic resin.

In general, vinyl acetate is generally used as the vinyl ester monomer in view of economy. The polymerization method may be any known polymerization method, for example, solution polymerization, suspension polymerization, emulsion polymerization, or bulk polymerization, and solution polymerization using methanol as a solvent is generally used. The reaction may be either a continuous or batch type.

As a method for introducing ethylene into the copolymer, ordinary ethylene pressure polymerization can be carried out. The content of ethylene units can be controlled depending on the pressure of ethylene, and is usually from 25 to 80kg/cm ² Is selected according to the target ethylene content.

The saponification of the ethylene-vinyl ester copolymer thus obtained can also be carried out by a known method. The saponification may be carried out by using an alkali catalyst or an acid catalyst in a state where the copolymer obtained in the above is dissolved in an alcohol or a hydrous alcohol.

The EVOH resin synthesized as above contains mainly ethylene units and vinyl alcohol structural units, and contains some amounts of vinyl ester structural units remaining without saponification.

The EVOH resin used as a material of the EVOH resin pellet may further include: structural units derived from the comonomers shown below. Examples of the comonomer include: alpha-olefins such as propylene, isobutylene, alpha-octene, alpha-dodecene, and alpha-octadecene; hydroxyl group-containing α -olefins such as 3-buten-1-ol, 4-penten-1-ol and 3-buten-1,2-diol, and hydroxyl group-containing α -olefin derivatives such as esters and acylates thereof; hydroxyalkyl vinylenes such as 2-methylenepropane-1,3-diol and 3-methylenepentane-1,5-diol; hydroxyalkyl vinylidene diacetates such as 1,3-diacetoxy-2-methylene propane, 1,3-dipropyloxy-2-methylene propane, and 1,3-dibutyloxy-2-methylene propane; unsaturated carboxylic acids or salts thereof, partial alkyl esters, complete alkyl esters, nitriles, amides, anhydrides; an unsaturated sulfonic acid or a salt thereof; a vinyl silane compound; vinyl chloride; styrene; and the like.

Furthermore, an EVOH-based resin "post-modified" by urethanization, acetalization, cyanoethylation, oxyalkylation or the like may be used as the EVOH resin.

Of the above modified products, EVOH resins having a primary hydroxyl group introduced into the side chain by copolymerization are preferred in view of their excellent post-formability such as stretching treatment and vacuum/pressure-air forming, and among them, EVOH resins having a1,2-diol structure in the side chain are preferred.

The content of ethylene units (ethylene unit content) in the EVOH resin constituting the EVOH resin pellet group used in the molding material is preferably 20 to 60 mol%. If the ethylene unit content is too low, the gas barrier properties and the appearance properties of the obtained molded article, particularly a stretched film, tend to be lowered at high humidity, and conversely, if it is too high, the gas barrier properties of the stretched film tend to be lowered.

The saponification degree of the vinyl ester component in the EVOH resin constituting the EVOH resin pellet group used in the molding material is preferably 90 mol% or more, particularly preferably 93 to 99.99 mol%, and further preferably 98 to 99.99 mol%. If the saponification degree is too low, the gas barrier property, moisture resistance and the like of the stretched film tend to be lowered.

The Melt Flow Rate (MFR) (210 ℃ C., load 2160 g) of the EVOH resin constituting the EVOH resin pellet group used in the molding material is preferably 1 to 100g/10 min, particularly preferably 2 to 50g/10 min, and further preferably 3 to 30g/10 min. If the MFR is too large, the mechanical strength of the molded article tends to be deteriorated, and if it is too small, the extrusion processability during molding tends to be deteriorated.

The conditions for copolymerization to synthesize the above EVOH resin are not particularly limited, and the following conditions are preferably used.

The solvent used for the above copolymerization is generally a lower alcohol such as methanol, ethanol, propanol or butanol, or a ketone such as acetone or methyl ethyl ketone, and methanol is industrially suitably used.

The amount of the solvent to be used may be appropriately selected in consideration of the chain transfer constant of the solvent, depending on the degree of polymerization of the target copolymer, and for example, when the solvent is methanol, S (solvent)/M (monomer) =0.01 to 10 (weight ratio), and particularly preferably selected from a range of about 0.05 to 7 (weight ratio).

Examples of the polymerization catalyst used in the copolymerization include: known radical polymerization catalysts such as azobisisobutyronitrile, acetyl peroxide, benzoyl peroxide, lauroyl peroxide, and the like; peroxyesters such as tert-butyl peroxyneodecanoate, tert-butyl peroxypivalate, α' -bis (neodecanoylperoxide) diisopropylbenzene, cumyl peroxyneodecanoate, 1,1,3,3-tetramethylbutyl peroxyneodecanoate, 1-cyclohexyl-1-methylethyl peroxyneodecanoate, tert-hexyl peroxyneodecanoate, and tert-hexyl peroxypivalate; peroxydicarbonates such as di-n-propyl peroxydicarbonate, diisopropyl peroxydicarbonate, di-sec-butyl peroxydicarbonate, bis (4-tert-butylcyclohexyl) peroxydicarbonate, di-2-ethoxyethyl peroxydicarbonate, di (2-ethylhexyl) peroxydicarbonate, dimethoxybutyl peroxydicarbonate, and di (3-methyl-3-methoxybutylperoxy) dicarbonate; diacyl peroxides such as 3,3,5-trimethylhexanoyl peroxide, diisobutyryl peroxide, lauroyl peroxide, and the like; and low-temperature living radical polymerization catalysts.

The amount of the polymerization catalyst to be used varies depending on the kind of the catalyst, and is not generally determined, and is arbitrarily selected depending on the polymerization rate. For example, when azobisisobutyronitrile or acetyl peroxide is used, the amount is preferably 10 to 2000ppm, and particularly preferably 50 to 1000ppm, based on the vinyl ester monomer.

It is preferable to co-exist a hydroxy lactone compound or a hydroxy carboxylic acid together with the above catalyst. Thereby, coloring of the pellets can be suppressed. The hydroxy lactone compound is not particularly limited as long as it has a lactone ring and a hydroxyl group in the molecule, and examples thereof include: l-ascorbic acid and erythorbic acid are suitably used, and glycolic acid, lactic acid, glyceric acid, malic acid, tartaric acid, citric acid, salicylic acid and the like are exemplified as hydroxycarboxylic acids, and citric acid is suitably used.

The amount of the above-mentioned hydroxy lactone compound or hydroxy carboxylic acid used is preferably 0.0001 to 0.1 part by weight, particularly preferably 0.0005 to 0.05 part by weight, and further preferably 0.001 to 0.03 part by weight, based on 100 parts by weight of the vinyl ester monomer, in both cases of the batch type and the continuous type. If the amount is too small, the effect of coexistence tends to be insufficiently obtained, and conversely, if it is too large, the polymerization of the vinyl ester monomer tends to be inhibited. When the above-mentioned compound is charged into the polymerization system, it is not particularly limited, and it is usually diluted with a solvent such as a lower aliphatic alcohol (methanol, ethanol, propanol, tert-butanol, etc.), an aliphatic ester containing a vinyl ester monomer (methyl acetate, ethyl acetate, etc.), water, or a mixed solvent thereof, and charged into the polymerization reaction system.

The copolymerization reaction cannot be generally determined depending on the solvent and pressure used, and is usually carried out at a temperature of not higher than the boiling point of the solvent, preferably 40 to 80 ℃ and particularly preferably 55 to 80 ℃. If the temperature is too low, polymerization takes a long time, and if the polymerization time is to be shortened, a large amount of catalyst is required, whereas if the temperature is too high, polymerization control becomes difficult, which is not preferable.

The polymerization time is preferably 4 to 10 hours (particularly 6 to 9 hours) in the case of a batch system. If the polymerization time is too short, the polymerization temperature must be increased or the amount of the catalyst must be set large, whereas if the polymerization time is too long, it is not preferable from the viewpoint of productivity. In the case of the continuous type, the average residence time in the polymerization tank is preferably 2 to 8 hours (particularly 2 to 6 hours), and if the residence time is too short, the polymerization temperature must be increased or the amount of the catalyst must be set large, whereas if the residence time is too long, there is a problem in productivity, which is not preferable.

The polymerization rate (vinyl ester monomer) is set as high as possible within a range in which polymerization can be controlled from the viewpoint of productivity, and is preferably 20 to 90%. If the polymerization rate is too low, there are problems such as productivity and the presence of a large amount of unpolymerized vinyl acetate monomer, whereas if it is too high, polymerization control becomes difficult, which is not preferable.

After the polymerization is carried out for a predetermined time and a predetermined polymerization rate is reached, a polymerization inhibitor is added as necessary to evaporate and remove unreacted ethylene gas, and then unreacted vinyl ester is discharged.

As a method for removing unreacted vinyl ester from an ethylene-vinyl ester copolymer from which ethylene is removed by evaporation, for example, the following method and the like are employed: the copolymer solution is continuously supplied from the top of a column packed with Raschig rings (Raschig rings) at a constant rate, while an organic solvent vapor such as methanol is blown from the bottom of the column, a mixed vapor of the organic solvent such as methanol and unreacted vinyl ester is distilled off from the top of the column, and the copolymer solution from which the unreacted vinyl ester has been removed from the bottom of the column is taken out.

An alkali catalyst is added to the copolymer solution from which unreacted vinyl ester has been removed, to saponify a vinyl ester component in the copolymer.

In the saponification, the copolymer obtained in the above is dissolved in an alcohol or aqueous alcohol, and the saponification is performed using an alkali catalyst or an acid catalyst. Examples of the alcohol include methanol, ethanol, propanol, and tert-butanol, and methanol is particularly preferably used. The concentration of the copolymer in the alcohol may be appropriately selected depending on the viscosity of the system, and is usually selected from the range of 10 to 60% by weight. Examples of the catalyst used in saponification include: alkali catalysts such as hydroxides and alkoxides of alkali metals including sodium hydroxide, potassium hydroxide, sodium methoxide, sodium ethoxide, potassium methoxide, and lithium methoxide; sulfuric acid, hydrochloric acid, nitric acid, methanesulfonic acid, zeolite, cation exchange resin, and the like.

The amount of the saponification catalyst used may be appropriately selected depending on the saponification method, the desired saponification degree, and the like, and when an alkali catalyst is used, it is usually preferably 0.001 to 0.1 equivalent, and particularly preferably 0.005 to 0.05 equivalent to the total amount of monomers such as vinyl ester monomers. The saponification method may be any of batch saponification, continuous saponification on a belt, and continuous saponification in a column depending on the desired saponification degree, and it is preferable to use column saponification under a constant pressure because the amount of the alkali catalyst can be reduced during saponification and the saponification reaction can be easily advanced with high efficiency.

The pressure at the time of saponification cannot be generally determined depending on the ethylene unit content of the objective EVOH resin, and is selected from the range of 2 to 7kg/cm ² The saponification temperature is preferably 80 to 150 ℃, particularly preferably 100 to 130 ℃, and the saponification time is selected from 0.5 to 3 hours. It is preferable that the EVOH resin after the reaction be neutralized as necessary.

As the EVOH resin which becomes a raw material of the pellet, an EVOH resin composition in which a compounding agent generally compounded with EVOH resin, for example, a heat stabilizer, an antioxidant, an antistatic agent, a colorant, an ultraviolet absorber, a plasticizer, a light stabilizer, a surfactant, an antibacterial agent, a desiccant, an anti-blocking agent, a flame retardant, a crosslinking agent, a curing agent, a foaming agent, a crystal nucleating agent, an antifogging agent, an additive for biodegradation, a silane coupling agent, an oxygen absorbent, and the like are added may be used within a range not to impair the effects of the present invention, in the EVOH resin synthesized as described above.

(2) Manufacture of pellets

Each pellet taken out from the group of EVOH resin pellets constituting the molding material of the present invention is a pellet having a surface constituted by one closed curved surface. The pellets described above are in other words the following pellets: 1) Granular materials whose surface is entirely composed of curved surfaces; 2) A pellet having no corner formed by joining a plurality of faces; 3) The cross section of the pellet at any position is not rectangular, but is preferably elliptical perpendicular to the major axis of the pellet. Such pellets are generally obtained by melt-extruding and cutting an EVOH resin in a molten state.

When the EVOH resin is cut with a cutter while it is melt-extruded and cooled to solidify, the edge portion formed by the cutting may sag during the cooling and solidifying process and also may be spherical due to surface tension, so that pellets having a single closed curved surface as a whole can be obtained. Specifically, depending on the shape (usually quadrangular prism or cylindrical) at the time of melt extrusion, pellets having a shape such as a sphere including an ellipsoid, a disc, a rugby, a chestnut, or pellets having a very small teardrop shape or a spherical shape can be obtained.

The invention has the following characteristics: pellets having a shape such as a sphere, a disk, a rugby, or a chestnut, including an ellipsoid, which have been known in the past, are used as a molding material in a pellet group having a shape closer to a sphere and having less variation in shape.

In order to obtain the pellet group used in the molding material of the present invention, the following methods can be exemplified.

Method 1 screening pellets having a shape such as a sphere, a disc, a rugby, or a chestnut shape, including a conventionally known ellipsoid, and selecting pellets having a desired ratio of major axis to minor axis to obtain the pellet group

Method 2. Lowering the peripheral speed of the cutter blade in cutting EVOH resin in a molten state

Method 3 reducing the number of revolutions of a cutter blade for cutting EVOH resin in a molten state

Method 4. Lowering the resin discharge linear velocity when cutting EVOH resin in a molten state

Method 5. The pellets having high flexibility immediately after cutting the EVOH resin in a molten state are immersed in a poor solvent or a low-temperature solvent and sufficiently solidified

These methods all lower the productivity, and therefore, they have not been used in the prior art, but they are expected to be used in the present invention, and thus a group of pellets having the above-mentioned characteristics can be obtained. These may be used alone or in combination of two or more methods.

Among these, the methods 2, 3 and 4 described above, which are less in the reduction of the production efficiency, are preferable. When the methods 2, 3 and 4 are combined with the method 5, the productivity of the pellet group tends to increase.

The specific method for producing the pellets is described in detail below.

In order to produce pellets, as an EVOH resin raw material to be fed into a melt extruder, (i) a solution or slurry of an EVOH resin obtained by saponification in the above-mentioned synthesis method of an EVOH resin may be used as it is, or an EVOH resin aqueous composition after appropriately adjusting the water content of the solution or slurry; alternatively, (ii) pellets of EVOH resin obtained by strand cutting (dry EVOH resin pellets) may be melted and EVOH resin in the molten state (dry EVOH resin) may be used.

(2-1) use of an EVOH resin aqueous composition (paste) as a raw Material

When an aqueous EVOH resin composition (paste) is used as a raw material for pellets to be fed to an extruder, the aqueous EVOH resin composition preferably contains 0 to 10 parts by weight of an alcohol and 10 to 500 parts by weight of water per 100 parts by weight of EVOH resin.

When an EVOH resin aqueous composition having a large alcohol content is used, it is impossible to prevent evaporation of alcohol in the subsequent step, and it is difficult to maintain the working environment or the ambient environment. In addition, when the temperature of the pellet washing water is increased to remove the alcohol, pellets are likely to stick to each other, and conversely, the washing time of the washing at a low temperature becomes long, which causes a reduction in production efficiency.

On the other hand, when an EVOH resin aqueous composition having a large water content is used, when the composition is cut in a molten state, the cut pellets tend to be welded to each other or the pellet shape tends to be uneven, and conversely, when the water content is small, the EVOH resin aqueous composition tends to have insufficient fluidity and to decrease the productivity of the pellets.

The method for adjusting the water content of the EVOH resin aqueous composition for producing pellets is not particularly limited, and in order to increase the water content, there may be adopted: a method of spraying water to the resin, a method of immersing the resin in water, a method of contacting the resin with water vapor, and the like. Drying may be suitably performed to reduce the water content, and may be performed using, for example, a flow type hot air dryer and/or a static type hot air dryer. From the viewpoint of reducing uneven drying, a flow-type hot air dryer is preferably used. Further, from the viewpoint of suppressing thermal deterioration, it is preferable to set the drying temperature to 120 ℃ or lower.

The EVOH resin solution after saponification is usually obtained as a solution containing a large amount of alcohol, but the EVOH resin solution after saponification is brought into contact with water vapor, whereby an EVOH aqueous composition having a small alcohol content is taken out of a container and can be used as a raw material for producing pellets.

When the aqueous EVOH resin composition is fed into an extruder as a pellet raw material, the temperature of the aqueous EVOH resin composition in the extruder is preferably 70 to 170 ℃, particularly preferably 80 ℃ or higher, and more preferably 90 ℃ or higher and 170 ℃ or lower. If the temperature of the aqueous composition of EVOH resin is too low, the EVOH resin may not be completely melted, and if the temperature is too high, EVOH may be easily thermally deteriorated. The temperature of the resin composition is a temperature detected in the vicinity of the outlet at the tip end of the extruder by a temperature sensor provided in the barrel of the extruder.

The extruder to be used is not particularly limited, and the diameter of the nozzle is preferably 1 to 10mm, particularly preferably 2 to 5mm, from the viewpoint of ease of handling of pellets.

The number of blades of the cutter is preferably 2 to 8, particularly preferably 3 to 6.

The cutter blade is preferably attached so as to contact the discharge port of the die of the extruder, and the distance between the die and the cutter blade is 0mm, but may be about 0.01 to 0.2 mm.

The rotational speed of the cutter blade is preferably 50 to 2000rpm, particularly preferably 100 to 1100rpm, further preferably 200 to 1000rpm, and particularly preferably 500 to 1000rpm. When the above numerical value is within the above range, the molding material of the present invention tends to be obtained more efficiently.

The peripheral speed of the cutter blade is preferably 1 to 6 m/sec, particularly preferably 1 to 5 m/sec, and further preferably 1 to 3 m/sec. When the above numerical value is within the above range, the molding material of the present invention tends to be obtained more efficiently.

The linear velocity of the resin discharged from the mold is preferably 10 to 200 m/sec, particularly preferably 50 to 150 m/sec, and more preferably 60 to 100 m/sec. When the above numerical value is within the above range, the molding material of the present invention tends to be obtained more efficiently.

The size and shape of the pellet can be adjusted by appropriately adjusting the diameter of the nozzle, the number of blades of the cutter, the rotation speed of the cutter, and the like.

The EVOH resin aqueous composition extruded from the die, that is, the EVOH resin in a molten state is cut before cooling to solidify (hot cutting method). The thermal cutting method may be cutting in the atmosphere (air cutting method); the extrusion is carried out in a cutter installation vessel filled with cooling water, and cutting is carried out in cooling water (underwater cutting method), and the underwater cutting method is preferable. The underwater cutting method can be performed, for example, by using an underwater pelletizer.

The cooling water is not limited to water. It is also possible to use: a water/alcohol mixture; aromatic hydrocarbons such as benzene; ketones such as acetone and methyl ethyl ketone; ethers such as dipropyl ether; organic esters such as methyl acetate, ethyl acetate, and methyl propionate; and the like. Among these, water or a water/alcohol mixed solution is preferably used in view of easy handling. The water/alcohol (weight ratio) in the water/alcohol mixed solution is usually 90/10 to 99/1. As the alcohol, lower alcohols such as methanol, ethanol, and propanol can be used, and methanol is industrially preferably used.

The temperature of the cooling water in the underwater cutting system is such a temperature that the EVOH resin extruded in a molten state does not instantaneously solidify (solidify), and when the EVOH resin is brought into contact with the cooling water before cutting, the temperature of the cooling water is preferably-20 to 50 ℃, and particularly preferably-5 to 30 ℃.

(2-2) use of Dry EVOH resin pellets as a raw Material

When dry EVOH resin pellets (having a water content of usually 0.5 wt% or less) are used as a raw material of the EVOH resin pellets constituting the molding material of the present invention, the dry EVOH resin pellets are fed into an extrusion kneader and melt-extruded.

The size and shape of the dry EVOH resin pellets used as a raw material are not particularly limited.

The temperature of the EVOH resin in the extruder-kneader must be set higher than that of the aqueous EVOH resin composition. Specifically, it is preferably from 150 to 300 ℃, particularly preferably from 200 to 285 ℃, and further preferably from 240 to 270 ℃. When the set temperature is too low, the EVOH resin pellets tend not to be completely melted. Conversely, if the EVOH resin temperature is too high, the EVOH resin tends to be easily thermally degraded. The resin temperature is a temperature detected in the vicinity of the outlet of the extruder distal end portion by a temperature sensor provided in the extruder barrel.

The extruder to be used is not particularly limited, and the diameter of the nozzle is preferably 1 to 5mm, particularly preferably 2 to 3.5mm, from the viewpoint of ease of handling of pellets.

The rotational speed of the cutter blade is preferably 10 to 2000rpm, particularly preferably 50 to 1100rpm, further preferably 100 to 1000rpm, and particularly preferably 200 to 1000rpm. When the above numerical value is within the above range, the molding material of the present invention tends to be obtained more efficiently.

The linear velocity of the resin discharged from the mold is preferably 10 to 200 m/sec, particularly preferably 50 to 150 m/sec, and further preferably 60 to 100 m/sec. When the above numerical value is within the above range, the molding material of the present invention tends to be obtained more efficiently.

The shape of the pellet is adjusted by appropriately adjusting the diameter of the nozzle, the number of blades of the cutter, the rotation speed of the cutter, and the like.

As in the case of using the EVOH resin aqueous composition as a raw material, the cutting in the molten state may be carried out by either of an air-cut method and an underwater-cut method, and the underwater-cut method is preferred. As the cooling water in the underwater cutting system, the cooling water exemplified in the case of using the EVOH resin aqueous composition as a raw material can be used. However, in the case of using dry EVOH resin pellets as a raw material, solidification is more likely than in the case of using an EVOH resin aqueous composition as a raw material, and therefore, the temperature of the cooling water in the underwater cutting system is higher than that in the case of using an EVOH resin aqueous composition as a raw material, and is preferably 0 to 90 ℃, and particularly preferably 20 to 70 ℃.

The pellets obtained as above are preferably subjected to water washing. In particular, since pellets from which an aqueous EVOH resin composition is obtained as a raw material often contain an alkali metal salt of a residue of a catalyst used in saponification, in the case of the pellets, washing with water is generally performed in order to prevent a reduction in quality against coloring and the like of a finally obtained molded product.

The washing with water is carried out in a water tank at 10 to 60 ℃. For example, it is preferable to use 200 to 1000 parts by weight (particularly preferably 300 to 600 parts by weight) of water per 100 parts by weight of the EVOH resin pellet and to carry out the reaction for 0.5 to 5 hours and 1 to 5 times (particularly preferably 1 time) at 20 to 50 ℃ (particularly preferably 25 to 35 ℃). By such washing with water, the content of alcohol, acetic acid, and sodium acetate having 5 or less carbon atoms in the EVOH resin can be adjusted, and oligomers and impurities can be removed.

The washing with water is usually carried out to adjust the amount of the alcohol having 5 or less carbon atoms to 0.0001 to 1 part by weight, the amount of acetic acid to 0.01 to 1 part by weight, and the amount of sodium acetate to 0.01 to 1 part by weight, based on 100 parts by weight of the EVOH resin pellet.

After washing with water, the EVOH resin pellets are brought into contact with an aqueous solution of an additive, if necessary.

Examples of the additives include organic acids such as acetic acid, propionic acid, butyric acid, lauric acid, stearic acid, oleic acid, behenic acid, and the like, and salts thereof such as alkali metal salts (sodium, potassium, and the like), alkaline earth metal salts (calcium, magnesium, and the like), zinc salts, and the like; and inorganic acids such as sulfuric acid, sulfurous acid, carbonic acid, phosphoric acid and boric acid, and salts thereof such as alkali metal salts (sodium, potassium, etc.), alkaline earth metal salts (calcium, magnesium, etc.) and zinc salts.

Among these, acetic acid, a boron compound containing boric acid and a salt thereof, an acetate, and a phosphate are particularly preferably added.

By bringing the EVOH resin pellets into contact with an aqueous solution of the additive, the EVOH resin pellets contain the additive, and thus various physical properties such as thermal stability during melt molding can be improved.

The method of contacting with the aqueous solution of the additive is carried out at 10 to 80 ℃ (particularly preferably 20 to 60 ℃, and more preferably 30 to 40 ℃) for 0.5 to 5 hours, and 1 to 3 times (particularly preferably 1 time) using 200 to 1000 parts by weight (particularly preferably 300 to 600 parts by weight) of an aqueous solution of the additive of 3% or less (particularly preferably 0.3 to 1.5%) per 100 parts by weight of the EVOH resin pellet.

By the operation of contacting with the aqueous solution of the additive, it is preferable that acetic acid is usually adjusted to 0.001 to 1 part by weight, a boron compound is adjusted to 0.001 to 1 part by weight in terms of boron (after ashing, analysis by ICP emission spectroscopy), and acetate and phosphate (including hydrogen phosphate) are adjusted to 0.0005 to 0.1 part by weight in terms of metal (after ashing, analysis by ICP emission spectroscopy), based on 100 parts by weight of the EVOH resin pellet.

After the above-described steps, a centrifugal separator is generally used in a solid-liquid separation method of pellets from water or an aqueous additive solution in terms of production efficiency.

The hydrous EVOH resin pellets with the concentrations of the respective components adjusted as described above were dried. The water content of the EVOH resin pellet after drying is preferably 1 wt% or less, particularly preferably 0.5 wt% or less.

As the drying method, various drying methods can be adopted, and examples thereof include: a method using a centrifugal dehydrator, a method of removing water during air transportation, a static drying method, a fluidized drying method, or the like, and a multi-step drying process combining several drying methods may be employed.

In particular, in the present invention, the pellets having high flexibility immediately after cutting tend to be sufficiently solidified by being immersed in a poor solvent or a low-temperature solvent, whereby the molding material of the present invention can be obtained more efficiently. Examples of the poor solvent include propanol, glycerol, diethyl ether, acetone, methyl ethyl ketone, ethyl acetate, pentane, carbon tetrachloride, dichloroethane, isobutyraldehyde, benzene, toluene, aniline, and silicone oil, and examples of the low-temperature solvent include water, a lower alcohol, and a hydrous alcohol. The temperature of the low-temperature solvent is usually 0 to 10 ℃.

The EVOH resin pellet thus obtained may be blended with, if necessary, within a range not to hinder the effect of the present invention: examples of the compounding agent generally compounded in EVOH resins include antioxidants, antistatic agents, colorants, ultraviolet absorbers, lubricants, plasticizers, light stabilizers, surfactants, antibacterial agents, drying agents, antiblocking agents, flame retardants, crosslinking agents, curing agents, foaming agents, crystal nucleating agents, antifogging agents, additives for biodegradation, silane coupling agents, and oxygen absorbers.

< use of Molding Material >

The molding material of the present invention having the above-described structure is excellent in feeding properties, and therefore, is preferably used as a melt molding material for producing an EVOH resin molded product.

The molding material of the present invention is suitably used as a molding material for melt molding, particularly melt extrusion of films, sheets, fibers and the like. As the melt molding method, extrusion molding methods (T-die extrusion, inflation extrusion, blow molding, melt spinning, profile extrusion, and the like) and injection molding methods are mainly used.

The conditions and type of the molding machine used are not particularly limited, and an extruder is generally used. The melt plasticizing section of the extruder may be either a screw type or a ram type, and a screw type is preferred. The extruder can be vertical or horizontal, and can be single screw rod type or double screw rod type. The L/D (screw length/screw diameter) of the screw and the compression ratio (C) are also not particularly limited, and from the viewpoint of more effectively obtaining the effect of the present invention, L/D is preferably selected in the range of 20 to 35, particularly preferably 25 to 30, and C is preferably selected in the range of 1.5 to 8, particularly preferably 2 to 5.

When the molding material of the present invention is used, for example, when the rotation speed of the screw of the extruder is low and friction between the screw and the molding material is likely to occur, the feeding property is also improved. Therefore, the screw rotation speed of the extruder is preferably 10 to 100rpm, particularly preferably 20 to 90rpm, and further preferably 30 to 60rpm.

The melt molding temperature is selected from the range of 150 to 300 ℃.

The film or sheet obtained by molding can be used for various applications as it is, and is generally used by laminating with another substrate to form a laminate for further improvement in strength or for imparting other functions. The EVOH resin film, sheet or laminate thereof obtained using the molding material of the present invention can be used as a packaging material such as a food packaging material, an industrial drug packaging material, an agricultural drug packaging material, etc. due to its excellent gas barrier property. Further, the EVOH resin film, sheet or laminate thereof may be further formed into a cup, bottle or the like by secondary molding.

As other substrates used in the laminate, thermoplastic resins are useful. Examples of the thermoplastic resin include: polyethylenes such as linear low-density polyethylene, ultra-low-density polyethylene, medium-density polyethylene, and high-density polyethylene; polyolefins such as polypropylene, ethylene-propylene (block and random) copolymers, propylene- α -olefin (α -olefin having 4 to 20 carbon atoms) copolymers, polybutene, and polypentene; grafted polyolefins obtained by graft-modifying these polyolefins with an unsaturated carboxylic acid or an ester thereof; an ionomer; ethylene-vinyl acetate copolymers; ethylene-acrylic acid copolymers; ethylene-acrylic ester copolymers; a polyester resin; polyamide resins (including copolyamides); polyvinyl chloride; polyvinylidene chloride; an acrylic resin; polystyrene; a vinyl ester resin; a polyester elastomer; a polyurethane elastomer; halogenated polyolefins such as chlorinated polyethylene and chlorinated polypropylene; aromatic or aliphatic polyketones; polyols obtained by reducing them; for example, polyolefin-based resins and polyamide-based resins are preferable from the viewpoint of practical properties (particularly strength) of the laminate, and polyethylene and polypropylene are particularly preferable.

These base resin may contain, within a range not to impair the gist of the present invention: conventionally known antioxidants, antistatic agents, lubricants, core materials, antiblocking agents, ultraviolet absorbers, waxes, and the like.

The method for laminating the resin composition of the present invention with another substrate can be performed by a known method. For example, the following methods may be mentioned: a method of melt extrusion laminating another substrate on a film, sheet or the like of the resin composition of the present invention; a method of melt extrusion laminating the resin on other substrates in contrast; a method of coextruding the resin with other base materials; a method of dry laminating the resin (layer) and another substrate (layer) with a known adhesive such as an organic titanium compound, an isocyanate compound, a polyester compound, or a polyurethane compound; a method of removing the solvent after coating the solution of the resin on another substrate; and the like.

Among them, a method of performing coextrusion is preferable from the viewpoint of cost and environment. When the molding material of the present invention is used, it can be used for extrusion molding with other thermoplastic resins. The molding material of the present invention is excellent in film moldability, and therefore, variation in the width of a melt-extruded film or the like is suppressed, and therefore, the molding material can be suitably used for producing a multilayer structure for melt coextrusion with other thermoplastic resins.

The layers of the laminate were constructed as follows: when the EVOH resin layer derived from the molding material of the present invention is A (A1, A2, …) and the thermoplastic resin layer is B (B1, B2, …), the resin layer may have not only a two-layer structure of A/B but also any combination of B/A/B, A/B/A, A/A2/B, A/B1/B2, B2/B1/A/B1/B2, and the like. When a recycled layer comprising a mixture of the EVOH resin and the thermoplastic resin, obtained by remelting end portions, defective products, and the like generated in the process of producing the laminate, is R, B/R/A, B/R/a/B, B/R/a/R/B, B/a/R/a/B, B/R/a/R/B, and the like, may be formed.

As described above, the laminate is preferably subjected to a heat stretching treatment for further improving the physical properties. For the heat stretching treatment and the like, a known stretching method can be used.

As the stretching method, in addition to a roll stretching method, a tenter stretching method, a tubular stretching method, a stretch blow molding method, and the like, a method having a high stretching ratio in deep drawing, vacuum forming, and the like can be used. In the case of biaxial stretching, any of simultaneous biaxial stretching and sequential biaxial stretching may be employed. The stretching temperature is preferably selected from the range of about 80 to 170 ℃ and particularly preferably about 100 to 160 ℃.

After the stretching treatment, heat fixation is preferably performed. The heat-fixing can be carried out by a known method, and the stretched film is heat-treated at 80 to 170 ℃ (particularly preferably 100 to 160 ℃) for about 2 to 600 seconds while being held in a stretched state.

When the laminated film is used for the purpose of heat-shrink packaging raw meat, processed meat, cheese, or the like, a product film is formed without heat-setting after stretching, and the raw meat, processed meat, cheese, or the like is stored in the film, and heat-treated at 50 to 130 ℃ (particularly preferably 70 to 120 ℃) for about 2 to 300 seconds to heat-shrink the film and perform close-fitting packaging.

The shape of the laminate is not particularly limited, and examples thereof include a film, a sheet, a tape, a bottle, a tube, a filament, and a profiled extrudate. The laminate may be subjected to heat treatment, cooling treatment, rolling treatment, printing treatment, dry lamination treatment, solution or melt coating treatment, bag making processing, deep drawing processing, box processing, pipe processing, dividing processing, and the like as necessary.

Examples

The present invention will be described in further detail below with reference to examples, but the present invention is not limited to these examples.

< production of EVOH resin pellets >

(1) EVOH resin pellet group of examples

A water/methanol mixed solution of EVOH resin having an ethylene content of 29 mol% and a saponification degree of 99.7 mol% (water/methanol =40/60 (weight ratio), EVOH resin concentration of 45%) was used as a raw material. The above water-containing EVOH was charged into an extruder and melt-kneaded, and the melt was extruded through a die having 3 holes (hole diameter: 2.5 mm) and cut with a hot cutter having 3 blades. The resin temperature at this time was 60 ℃. The flow rate of the circulating water of the cutter was 42 liters/minute. At this time, the linear speed of discharge from the die was 32.9 m/min, the rotational speed of the cutter blade was 900rpm, and the peripheral speed was 2.0 m/sec.

The obtained pellets were dried at 122 ℃ for 16 hours in a flow dryer, to thereby obtain an EVOH resin pellet group of examples. The water content of the pellet group was 0.22 wt%. From the obtained pellet group, 20 pellets were taken out, and the major axis and the minor axis were measured by the above-mentioned measuring method, and the average value thereof was calculated. Further, for 20 pellets, the ratio of the major axis to the minor axis was determined, and the average value and the standard deviation were calculated. Namely, the EVOH resin pellet groups of the examples were: the average of the major axis was 3.9mm, the average of the minor axis was 3.0mm, the average of the major axis/minor axis ratio was 1.29, and the standard deviation of the major axis/minor axis ratio was 0.11.

(2) EVOH resin pellet group of comparative example

A water/methanol mixed solution of EVOH resin having an ethylene content of 29 mol% and a saponification degree of 99.7 mol% (water/methanol =40/60 (weight ratio), EVOH resin concentration of 45%) was used as a raw material. The above water-containing EVOH was charged into an extruder and melt-kneaded, and the melt was extruded through a die having 3 holes (hole diameter: 2.5 mm) and cut with a hot cutter having 5 blades. The resin temperature at this time was 60 ℃. The flow rate of the circulating water of the cutter was 42 liters/minute. At this time, the linear speed of discharge from the die was 56.9 m/min, the rotational speed of the cutter blade was 1800rpm, and the peripheral speed was 4.1 m/sec.

The obtained pellets were dried at 122 ℃ for 16 hours in a flow dryer to obtain an EVOH resin pellet group of comparative example. The water content of the pellet group was 0.14 wt%. From the obtained pellet group, 20 pellets were taken out, and the major axis and the minor axis were measured by the above-mentioned measuring method, and the average value thereof was calculated. Further, for 20 pellets, the ratio of the major axis to the minor axis was determined, and the average value and the standard deviation were calculated. Namely, EVOH resin pellets of comparative examples were: the average of the major axis was 4.6mm, the average of the minor axis was 2.8mm, the average of the major axis/minor axis ratio was 1.67, and the standard deviation of the major axis/minor axis ratio was 0.15.

< evaluation method >

A molding material was fed into an extruder, and a film was formed under the following conditions to form an EVOH resin film having a thickness of 50 μm.

Inner diameter of the screw: 40mm

L/D：28

Screw compression ratio: 3.0

And (3) T mode: clothes hanger type

The width of the die is as follows: 450mm

Screw rotation speed of extruder: 40rpm or 80rpm

Extrusion temperature (. Degree. C.): C1/C2/C3/C4/H (head)/AD (adapter)/D (mold) =180/190/220/220/220/220/220

(feeding property)

An auscultation rod was installed at the lower part of the hopper of the extruder, and the number of abnormal sounds generated from the extruder in 20 seconds was counted. The number of abnormal sounds was counted 10 times every 10 seconds, and the average of the number of abnormal sounds was calculated. The more the abnormal sound occurs, the more the load is applied to the screw of the extruder.

(discharge amount)

The weight of each 2-minute EVOH resin film taken was measured 20 minutes, 40 minutes, and 60 minutes after the start of film formation. In the results of 3 measurements, the maximum value was defined as Dmax and the minimum value was defined as Dmin. The larger the difference between Dmax and Dmin and the larger the ratio between Dmax and Dmin, the more unstable the discharge, and the more unstable the extrusion molding can be performed.

(feeding property)

[ Table 1]

When the rotation speed of the screw was 40rpm, the abnormal sound occurred 2 times in the comparative example, but the abnormal sound did not occur in the example. In addition, when the rotation speed of the screw was 80rpm, the abnormal sound occurred 3 times in the comparative example, and only 1 time in the example. In this example, the number of abnormal sounds was reduced, and it was found that the load on the screw of the extruder was reduced.

(difference in discharge amount: dmax-Dmin)

[ Table 2]

(ratio of discharge amounts: dmax/Dmin)

[ Table 3]

The examples are smaller than the comparative examples in the ratio between the difference in the discharge amount and the discharge amount, and therefore, it is understood that the molten resin is stably discharged in the examples, and stable extrusion molding is performed.

Industrial applicability

The molding material of the present invention is excellent in charging properties when it is subjected to melt molding, and therefore, is advantageous in improving the working environment in the production site and reducing the load on the melt extruder, and therefore, it is preferably used in the production site.

Description of the reference numerals

a major diameter (maximum outer diameter of pellet)

Maximum diameter of b section

c minor axis (minimum diameter of cross section)

Section F

P pellets

Claims

1. A molding material comprising a pellet group containing at least 20 pellets of an ethylene-vinyl ester copolymer saponified material,

each of the pellets constituting the ethylene-vinyl ester copolymer saponified material pellet group is a pellet having a surface formed of one closed curved surface,

when the maximum outer diameter of the pellet is a major diameter and the minimum diameter of a cross section having the maximum area in a cross section perpendicular to the major diameter is a minor diameter, the average value of the major diameter/minor diameter ratio of 20 pellets taken out from the pellet group is 1.6 or less and the standard deviation of the major diameter/minor diameter ratio is 0.13 or less, and the average value of the major diameter is 1 to 20mm and the average value of the minor diameter is 1 to 10mm among the 20 pellets taken out from the pellet group.

2. The molding material according to claim 1, wherein each of the pellets constituting the ethylene-vinyl ester copolymer saponified material pellet group is a pellet having an elliptical cross section perpendicular to the major axis.

3. The molding material according to claim 1 or 2, wherein the water content of the pellet group is 0.5 wt% or less.

4. A molding method comprising feeding the molding material according to any one of claims 1 to 3 to an extruder having a screw rotation speed of 10 to 100rpm, and molding the molding material into a molded article.

5. The molding method according to claim 4, wherein the peripheral speed of the cutter knife is 1 to 6 m/sec.